Ability to select ALL in a multi-select field

I would like to have the ability for a user to select all values in a multi-select field by checking a single checkbox rather than checking each of the individual values that are available. For example, we have modified one of the Opportunity user fields on the User Fields tab on the Opportunity detail screen so that the field is multi-select and the options are all 50 US states. We have instances in which we need to select all states. The user currently has to click on all 50 values for this field.

A single checkbox that would automatically select all available values would save quite a bit of time.

I was told by support that this option does not exist today. If there is a way to do this, please let me know.